Machine-switching telephone-exchange system



Jan. 8, 1924. 1,486,206

H. HOFFMANN.

MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM I Filed Dem-.24, 1920 5Sheets-sheaf; I

aim)

Jan. 8, 1924.

H. L. HOFFMANN MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Filed Dec.24, 1920 5 Sheets-Shaw 2 Wye/770i":

4 a Wm Jan. 8, 1924. 1,480,206

H. L. HOFFMANN MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Filed Dec.24. 1920 5 Eheets-Sheet 4- Hen/y L. Hoff mm 513 WW.-

Jan. 8, 1924. 1,480,206

H. L. HOFFMANN MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Filed Dec.24, 1920 -5 sheet s-sheet s //7l /7 for: Men/"y 1.. #0799361? relay (notshown) to place theoperators telephone set in a monitoring position onthe cord. The operator now turns the dial 1) for the first digit of thewanted number. lhe dial in moving out of its normal position shortcircuits the relay B34 permitting the relay E72 to operate. Relay E-72in operating locks itself to battery and transfers the tip of the plugTT through the impulse springs of the dial D to the battery. The dial,in returning to normal, interrupts the battery to the tip of the plugcausing the impulse relay A.--2 of the trunk circuit of Fig. 2 tooperate in termittently, the number of times depending upon the digitinvolved. This impulse relay, in thus operating, causes the setting ofthe incoming selector (Fig. 3) at the distant automatic oflice whichthereupon automatically picks out an idle trunk in the selected level.This trunk includes the equipment shown in Fig. 3 and terminates in theselector shown in Fig 4;. When the operator has turned the dial for allthe digits involved which causes the last switch or con- I replaces hisreceiver, this lamp again lights as a disconnect signal.

If the called line is busy or if one of the selectors had failed to findan idle trunk, the lamp 100 will flash, the frequency of the flashesdepending upon the busy condition encountered. The toll operator inresponse to the flashing of the lamp removes the plug TT of the trunkand toll end of the cord from the toll switching jack TSJ, but beforeremoving the toll plug T from jack J,

v the operator by .means of her ringing key RK, rings on the toll lineterminating at the jack J to notify the distant calling operator thatthe line is clear. If the distant operator rings first, however, thetoll supervisory lamp 101 lights and when the operator actuateslistening key LK, or pulls out the plug T, this lamp is extinguished.

If the called subscriber can be reached only over a toll lineterminating at a toll position at a distant office, the intermediatetoll operator inserts the plug TT of the trunk and toll end in a tollline jack leading to such distant ofice and by means of her ringing keyBK rings out over the toll line to signal the distant operator at suchoffice having access to the line of the caller subscribed who thencompletes the connection.

When the calling toll operator applies ringing current to the trunk atthe termination of the conversation, the toll supervisory lamp 101lights until the listening key Lli is operated or the connection istaken down. The keys K and K serve, when operated, to disconnect eitherend of the cord from the operators telephone set when the operator istalkingon the other end.

More in detail, when the plug- T of the toll end is inserted in tollanswering jack J, relay E156 operates, in turn operating relay B162.Relay B162 opens the circuit of) relay E162 preventing the tollsupervisory lamp 101 from lighting. When the plug TT of the trunk andtoll end is inserted in toll switching trunk jack. TSJ leading to anincoming selector at automatic office, relay E-99 operates in serieswith relay E-155 and the right winding of relay 51-156. Relay Fi99disconnects the busy test equipment of the operators tel ephone set fromthe tip of the cord and connects the tip of the cord through to theringing key. Relay E-155 is marginal and does not operate at this timeon accountof the high resistance in the sleeve of the toll switchingtrunk circuit, and thus leaves the calling supervisory relay B4 .3bridged across the trunk. Ringing current applied by a distant tolloperator operates the alter nating current relay A196 which releasesrelay B162. The latter relay in releasing lights the toll supervisorylamp 101 and operates relay E-162 in parallel with the lamp. Relay15-162 locks up under the control of the listening key LK and relayE-156 so that the lamp remains lighted after the ringing ceases and therelay 13-162 is re-operated through the back contact of relay A196. Thelamp 101 may be extinguished by operating the l stening key whichreleases relay E-162 or by taking down the connection which releasesrelays E156 and E-162 Relay 13-162 is made slow in operating to guardagainst the possibility of lamp 101 being lighted by Morse impulses.Relay ,A.196 may be operated for a short time by Morse impulses andrelease relay B-162 momentarily. but the slow operating feature of therelay E162 will give relay B-162 time toreoperate before the relayl3l-162 operates and locks. When both ends of the cord. inserted in tollline acks terminating at toll board positions the marginal relay E155disconnects the calling supervisory relay B43 from the cord circuit. if,on. a through toll connection of this character the splitting key K isoperated to disconnect the trunk and toll end TT from the operatorstelephone set. relay R 4c? bridged across the trunk and toll end so thatit will operate when ringing current is received from the trunk and tollend and E 412.795, filed September 25, 19 20.

flash the lamp 100. 'When the splittingkey- K is in its" normal positionthis bridge for relay B'43 is opened.

Referring" 110W to Fig. 2 which represents a toll switchingtrunlioverwhich a connection" is extendedt'o' an automatic exchange, relay C2operates over its right hand Winding vlieu the operator inserts the plugTT into jack TSJ and by attracting its armature closes a loopcircuitleading to the impulse relay of the incoining selector. at suchexchange, which selector being Well known is not shown. It may beat thetype shown in application of R. L. Stokely. Serial Tie brushes 300,-301,-302 and multiples 303, 305, indicate such selector. l Vhen' thedialing ke DK is thrown and the dial is operated, relay Eli-42 operates,connecting relay 1 2 across the loop leadingto the inipulse relay of theincoming selector at the automatic o'ili'ce. Relay I2 in operatingcauses slow relay to operate, whi chire lay shunts the left-hand windingofrelay C2 whereupon the latter relay releases the circuit through itsright hand Winding being opened when relay'E72; Fig: 1, 013'- e'rate'sas the dial is moved out of its normal position. Relay D-2 in operatingoperates relay E-Q which locks up was ground'at the inner left contactot relay B2. now energ zed. Relay E 2 at ts vouterlett contact locks uprelay D'2, independently of.

its original ene'rgizing circ'uit which leads over the front contact ofrelay I2. The dial in restoring intermittently operates relays 94-2 andl-Qi relay" A-Q- interniittentlf" opening theflo op circuit to, the hitpulse relayot the incomingflselector. and relay I2 alternatelyojpening'aiid' closinga shunt path around'relay D2. If, during theoperation of buildingfup a connection, oueot the selectors fails to findan idle trunk in the selected group, it opens the loop circuit includingrelay I2. Relay I2 in closing its backeontact permanently shunts outrelay D-2.- Relay D- 2 infclosngits right hand contact operates. relayIl-2. Relay H2 locks up and connects interrupted battery ofinipul'sespenniinute to the Winding of relay C2in shunt of the rsistance F200. 'Relay Bl3in the cord (Fig. 1) follows these impulses andflashes the supervisory lamp lOO-tb', indicate to the operator the tailure to fin'djan' idle trunk.

in case the called line is busy, interrupter is connected in circuit toflash the lamp 100 at different rate to indicate" to the 0})- crater thebusy condition of the selected line.

In case the called subscribers'line'is found to be idle by theconnector5) this-conditicu causes the 'polar-i zed relay. F'-2 to ope ateand-cause'lamp 100 t'o're'main steadily lighted asaringingsignalwhen theop eraterre'storesthe key..DK. Relay F-2 in operating/alsoenergizesrelay ;G2 vhich cuts the trunkthrough, thus disconnecting .the,rela'yfs'C'2and A-2 from the circuit leading baclt to the tolloperatofisposition. H'aviiig described in a general manner the op rates.of the system a call will now we traceaui detail. v

The toll-operator, having been informed of'the nuinberof the Wanted lineand assiirii'iii g.thislineto be in a nearby auto:- mafia exchange,tests for an idle trunk by touching theltip' of her plug TT to thesle'eveof thejac-k TSJ of the tollsvvitching trunk in" the yvellkno vnmanner, and if she does not receive a clic-k in her receiver sheinseigts tlie plugzTT into the toll switching t'u'nk ja'ck'TSJ. Thefollowing circuit is thereupon closed to--operate relays*E-99q (Fig:1)iaiid B;2. free pole'of battery; relays E' 99 1 1 -155,- right windinggpr relay lie-15 6, sleeves of the plugran d j :fck', relayB"2'togroiind.; Relay E155 (lees not; operate in the-circuit, as stated.Relay E-15G is oper'ateddue to plug T being inserted-in jacleJ Relay.Ill-+99 in operating disconnects the operators busy testcircuit from thetip of .cordgancl connects the, two sides ot the ti'p otfthelineto'gether. 'Relay B-2- (Fig. 2); in]. operating pr'ep'are's certaincircuits Wliich'ivill 1 be traced later. This trunk will saw testbusy atthe other toll. operators positions due to battery applied to the sleevev nnltiple's' the sleeve of the plug [1. "The'ins'ertion' of the plugalso. closes the following circuit to energizerelay C2: free pole of.battery;;-resistance 200, right hand Windingof relay;C2, conductor 2 01a'rinature oQ of relay G 2, conductor 203', iiiiieinnoriiialcontact ofrelay. 130, ring of the" jacl; TSLring ot' thc plug TT,'condu to'ifl120, lower norrna-l contact or. ringing l: KK, right hand Winding ofretardation coil" 121, relay 13 -43," ujlllit'tlll'e and back contempt.relay"l$-155 which is not oper- Whe'nthe plug IT is inserted in a tolltrunk switching jack, butonly when it is insertedina toll line leadingto a toll positioh at afdistantfofii'ce, left hand Winding ofretardation c0il l2l; upper normal contact of ringing ke'y RK, armatureand-front contact of relay E, 9, conductor 102, left hand nor'nialcontact of relay E72, con-Q followingzl bridge' to operate the impulserelay tr te inc'oiri-ing''selector at the autoni'ati'c" oifice',conductor" 205, conductor 206,

outer left hand armature and back contact of relay H2, conductor 207,armature and front contact of relay C2, left hand winding of relay C2,conductors 208 and 209, inner right armature and front contact of relayl3-2, conductor 210,v polarized relay F2, conductor 211, conductor 212.The operator now throws the dialing and monitoring key DK, whereupon acircuit is closed to operate relay B34, Fig. 1, which in attracting itsarmature closes a circuit to connect the operators head set across thecord. She now rotates the dial D for the first digit of the wantednumber. The closure of the contact 104 of the dial as the dial moves offnormal shunts the relay B34, which permits the marginal relay E72 tooperate. Relay E-7 2 in attracting its right hand armature locks itselfto ground at a contact of the dialing key DK which when actuated remainsin its operated position until manually restored by the operator. RelayE72 in closing its left-hand contact opens the bridge containing relayB43 and connects the free pole of the bat tery through the impulsecontact 108 of the dial to the tip of the plug. The opening of the saidbridge opens the circuit heretofore traced through the right handwinding of relay C2. Marginal relay A-2 now operates in series with theimpulse contact of the dial, the circuit being as follows: free pole ofbattery, resistance 109, impulse contact 108, left hand armature andfront contact of relay E72, conductor 103, tip of the plug TT, tip ofthe jack TSJ, outer normal contact of relav 130, conductor 131, armature204 and back contact of relay G2, conductor 213 and relay A-2 to ground.Relay A2 in attracting its left hand armature bridges relay T2 acrossthe tip and ring of the trunk in parallel with the left hand winding ofrelay C 2. Relay T2 in attracting its armature closes a circuit tooperate relay D2 as follows: free pole of battery, resistance 214,conductor 215, relay D2, conductor 216, right armature and front contactof relay I'-2, conductor 217, contact 218 of relay G-2 to ground. RelayD 2 in attracting its left armature short circuits the left hand windingof relay C2 which thereupon releases, thus opening one of the bridges tothe impulse relay at the incoming selector and leaving bridged acrossthe circuit only relay 1 2. This bridge may be traced as follows:conductors 205 and 206, outer left hand armature and back contact ofrelay H2, conductor 207, conductor 208, relay T-2, left hand armatureand front contact of relay A2, conductor 211, conductor 212. Relay D2 atits right armature and front contact closes the following circuit tooperate relay E2: free pole of battery, relay E2, conductor 220, rightarmature and;

front contact of relay D2, conductor 221, conductors 222 and 228, innerleft armature and front contact of relay 13-2 to ground. Relay E-2 inattracting its inner right armature locks itself to grounded conductor222. The function of this relay will be later described. Dial D, Fig. 1,in returning to normal, interrupts at its impulse contact 108 thecircuit of the impulse relay A2, Fig. 2, which at its left armatureinterrupts the circuit of the impulse relay of the incoming selector anumber of times corresponding to the first digit of the wanted number.The incoming selector TS is thus set to the desired level and thenautomatically picks out an idle toll transmission selector shown inFigs.3 and 4. The terminals of this selector are designated 303, 304, 305.

The seizure of the toll transmission selector, Fig. 4, with which therelay and repeating coil equipmentof Fig. 3 is asso ciated, causes theclosure of the following circuit for impulse relay A-4, Fig. 4, of thetoll transmission selector: freepole of battery, right hand winding ofrelay A4, conductor 400, conductor 306, outer left armature and backcontact of relay B-3, conductor 307, contacts of relays F-3, and H-3,conductor 308, upper left-hand winding of repeating coil 309, conductor325, multiple terminal 303, brush 300, conductor 212, conductor 211,left armature and front contact of relay A2, relay 1-2, conductors 208,207, outer left hand armature and back contact of relay H-2, conductors206, 205,

brush 301, multiple terminal 304, conductor 326, lower left hand windingof the repeat ing coil, conductors 311, 312, contacts of relays H3 andF-3 and B3, conductor 313, conductor 401, through the left winding ofrelay A-5 to ground at the lower normal contact of the switch 402 whichis operated only on the eleventh rotary step of the transmissionselector. The impulse relay A--4 in attracting its right armatureenergizes slow relay B-4. This relay in attracting its left armatureapplies a ground over the sleeve wires 451 and 314 to multiple 305 tocause this trunk to test busy and to hold up the release relay of theincoming selector in the well known manner. When the relay B4 operatesit closes at its right hand armature the following circuit for relay D 3of the relay and repeating coil circuit, Fig. 3: ground, right armatureand front contact of relay B-4, conductors 403 and 418, conductor 404,conductor 405, contact 406 of re lay D-4, conductor 407, 315, outerright hand armature and back contact of relay F 3, conductor 316, relayD3 to free pole of battery.

The second operation of the dial by the operator transmits the seconddigit of the called line causing relay A-2, Fig. 2 to open anclclosethe'impulse-j circuit for therleiy'r A4, which in vibretiiig its right hand?armature transmits impul s'e's over the' fol lowing/ circuit 'to "thevertical magnet" 40 8" oi? the toll transmission selector: "gi 'olii'iclefi ri ht-armature and back coiit'act of 'relayf far-l, innerarmature and froii'thdlitact of relay 13 -4, conductor e09; armature*klOhfitl brick Contact of relay 'D-ge coii clucjtor $411,"- slow relayC4,; magnet 408to"free"pole"off battery. The brushes ofthe tolltrimsirii sien selector are thus elevitetl' to' the deeired'j level.When the dial returri's to nor'malaliclf maintains the relay 'A -2'ehergiz'etl', relity" PLe remains" energizeil and; after e slight inter1 slow relay C -e releases. l Vhh the relay C 4: op'ereted' o1r'the'ffirstiIhp1ils'e and the selector toolrits fir tfstep', relay" iY'-ioperated over "the" follotvin g circui tree pol ofhattery, relayE-'4,-uppe1'-- fc oiitact of 0% norm'elsit itch 415,conclt bt6r 41h,arm. cure anti front contact of relhy-C 4, f COHQJiCtOZ 4:17,con'tl'uotor 4:18, cohductor'lOil" to ground at the'rig'htarmelt ire'eiicl front Contact of relay Be In attrhctihg its inner armature, re1ayE *4-" locksl itSelf to the upper armature and hzick Contact of slowrela'y 1 -14:, this eirct i't'incli'icling the'hrmer: ture hack contact"01: rotary megfiet' 419; Upon the 'cessatiohhfthe in'ip'ulees" Mid'threlease of the slow relay (3- 'tl1ecir:ctiit er the rotaryniegnetiselos'ecl es'ffoll'ows :fr'ee {vole or bzitteryfmaghet' 41 9;outer allfiiittll'' and front contact of relay E'4'.' normal Contact ofrelzg C l, condi'ictor"417, coIiF opening the circuit of th'e rotarymagi-en. If the trunk is busy,reley' E-4 a'g'zuh energizes over thefollowing circuit 2' free poleofbelt tery, relay 13 upper 'cont'ctoh-Switch contact" of re- 1m lL- l conductor 425 'test brush426"to a L 1h r ground on the testvmu'lti'pie 4:2(5 Relay li 5. in attracting itsinner armature agtiihf leeks up through the upper armature and backContact of relay F-Ainncl atthe other" armature again closesthecircuit0f retnr y magnet Whichhdvances thei hrhs'heer to the net-1t trunk andat 'theencl ofit'stroke open, the looking; circuit o'hrelay'lfi f "whichin retracting its armature opens the circuit of the rotary megnetelfi. V

Asuming now that the 'selehtor' has" failed to find an idle trunk Inthateverltoh the eleventh rotary 'step,sWitoh 402is'0pemreaby the shaftof the selector and opens the &

bick coh ct 0f relay 13-4. Relay E-4 is marginal and doesnot operate inthis circuit in series with the relay D4. Relay D-4 in attracting itsarmatures 431 and 432 extends the talking conductors through to thetalking brushes 433 and 434. The attraction of the armature 423 of relayD4 grounds the test brush 426 and consequently test multiple 427 of theselected trunk, causing the same to test busy to other selectors. Thecontact 435 is made before the contact 406 is broken by the armature 437of the relay D-4. Consequently relay D3, Fig. 3, in the relay andrepeating coil equipment is maintained energized over the followingcircuit: free pole of battery, relay D3, conductor 316, outer rightarmature and back contact of relay F'3, conductor 315, conductor 407,contact 435, conductor 438, brush-439, multiple 440, control conductor441, conductor 500, conductor 501, armature 502 and back contact ofrelay K-5, conductor 503, sleeve conductor 550, conductor 442, multiple427, brush 426, conductor 425, lowermost armature and back contact ofrelay 1 -4, conductor 424, armature 423 and front contact of relay D4,conductor 418, conductor 403, to ground at the right armature and frontcontact of slow relay B4. Thus, the circuit for relay, D-3 (Fig. 3) ismaintained closed as the circuit is extended from switch to switch. Aswill hereafter appear, relay F+3 is not operated until the desired lineis found idle and seized, when it reverses the direction of current flowin the circuit leading back to the toll operators position to li 'ht thesupervisory lamp 100 to indicate to her the idle condition of the line,whereupon she will cause the connector to begin the automatic ringingoperation. The switch of Fig. 5 to which the connection has beenextended is a combination toll and local connectorcontaining multiplesof ordinary lines in its bank. This switch is accessible not only to thetoll transmission selectors of Fig. 4, but also to the local selectorswhich are used by the subscribers in building up their own localconnections. The seizure of the connector causes the dos ing of thefollowing circuit for the impulse relay A-5: free pole of battery, upperwinding of relay A5, conductor 504, conductor- 505, left winding of slowrelay J5, conductors 506 and 507, lowermost armature and back contact ofrelay K-5, ring conductor 546, conductor 443, multiple 444, brush 434,conductor 445, armature 432 and front contact of relay D4, left armatureand front contact of relay A-4, ring conductor 446, conductor 318, lowerarmatures and back contacts of relays K3 and M-3, lowerright handWinding of the repeating coil 309, resistance 319, inner left armatureand front contact of relay D3, resistance 320, outer left-hand armatureand front contact of relay D3, resistance 321, upper right hand windingof repeating coil 309, upper armatures and back contacts of relays M3and K3, tipconductors 322, 447, armature 431, and front contact of relayD4, conductor 448, brush 433, multiple 449, tip conductor 450, conductor510, upper armature and back contactof relay l5, conductor 511,conductor 512, lower winding of relay A5 to ground. Relays J5 and A-5operate in this circuit, the former at its innermost right armatureclosing a locking circuit for itself as follows: free pole of battery,right winding and right innermost armature and front contact of relayJ-5, conductor 514, conductor 531, conductor 515 to ground at thearmature 516, and front contact of slow relay B5 which is energized uponthe energization of the impulse relay A-5. Relay B-5 grounds the sleevewire 517, leading to the test multiples in the local selectors, thiscircuit leading from grounded armature 516, conductor 515, to conductor517. The return of the dial to normal transmitting the tens digit afterthe operation of transmitting the hundreds digit of the wanted numberinterrupts the circuit of relay A2, Fig. 2 which in turn interrupts thecircuit of the impulse relay A5, Fig. 5 which in vibrating its armaturestransmits impulses to the vertical magnet 518 of the connector over thefollowing circuit: free pole of battery, magnet 518, slow relay 519,right contact of off normal switch 520, conductor 521, lower armatureand front contact of relay 13-5 to ground at the armature and backcontact of the impulse relay A5. At the first step of the connector, theoff normal springs 520 are shifted and the succeeding impulses aretransmitted by way of the upper armature and front contact of relay 519and the contact 522 now closed at the off normal springs 520. Theselector brushes are thus lifted to the desired level and upon thecessation of the impulses, impulse relay 141-5 remains energized andrelay 519 in series with the vertical magnet releases preparing thecircuit of the rotary magnet 523. The units impulses pass through theback contact of the impulse relay A-5, lower armature and front contactof relay B--5, conductor 521, off normal contact 522, upper armature andback contact of slow relay 519, conductor 524, left armature and backcontact of relay G-5, conductor 525, uppermost armature and back contactof relay 11-5, rotary around into engagement with the desired line.

If this line is idle, potential is present on its test multiple 526through the cut 01% Wind ing of the line switch in accordance withwell-known systems such as that disclosed magnet 523 to free pole of Ibattery. The connector is thus stepped 1 ,aeegeee in Patent 1,159,855,issued Noveinber 9,1915, to T. G. Martin; and the "followingcircuit" isclosed to operate relay 'H+5: n'u'ultiple 526, brush 527, conductor 528,-right hand armature and back" contact of relay v12%5," conductor 529',upper Winding of relay H 5," conductor 580, right hand armature andbac'li' contact of relay Ge-5, conductor 531, conductor 5i5,-arinature516 of relay B+5"to' ground. Relay H-5 in attractingits. armature 532locks itself to the groundedsleeve' Wire 550 and extends this gro'undedcon-' ductor over conductor 533, middle right armature and front contactof relay J'5, conductor 53% to the relay Relay K-5 in attracting itsarmature 502 discon-= nects the grounded sleeve Wire 550fro1nthe"control lead 50'O -leading'baclz'to the relay D3, Fig.- 3 of the relay?and repeatingcoil equipment circuit. Re'lay'D'3, therefore releases andin retracting its righthand armature operates relay 1F 3,' FigJ3, over"the following circuit? free pole of battery, relay F3, rightarmature'and back contact of relay D'3, conductor 323, conductor 450,armature 423 'and' front contact of relay D- i,'conduct0rs 418, 4:03 toground at the ri htarmature" and frontcontact of relay B Relay F 3 inattracting its outer right armature closes a substitute ground to holdupthe slow relay F-5 to prevent ringing'from occurring at this time:grounchrighthand armature of'relay' E3, conductor 321, right armatureand back contact of relay B 3, outer right arrriature and front contactof relay Fi3,"control 'conductors 315, 107, contact 2315 o f'r'elay' Dl, conductor 438, brush 439', multiplettO, conductor 14-1, conductoreodrmntcontact'and armature and lowerfwinding of relay F-5 to free poleof battery. Relay F5 was energized upon the first impulse to thevertical magnet, this circuit being'as follovvs tree pole of battery,lower 'wi'nd'ingot relay F-5, lower armature and front contact of" slowrelay 519,inner1nostright hand arma ture and front contact of relay J 5,conductor 51-1, conductors and 515 toground' at the upper inner armatureand front con act of relay B5. VV'hen' energize'drelay F--5 lockedby Wayof 'its armature 535; and front contact, conductor 501, armature 502 andback contact of relay K-'5' to" grounded sleeve Wire 550."Consequently," the operation of relay K-5 to cause the re-' versal ofdirection of the currentfiovifin the loop leading ba'ckto the'tolloperators position opened the circuitof sloW'rel-ay 5' and unless asubstitute circuit was provided for holding it up" the ringing operationwould autornatically take place" This is'prevented by applying asubstitute ground as described to the control conductor 500over thecircuit traced to" ho'ldthe relay F'5 until the operator,by'depressin-g-a"1 ey' as "tracting' its armatures" operates the lastdigit, I theopera'tor' restoresher dial 'ing"ke'y DECwhichrele'asesfrelay E-72 as described- Whi'c'h' disconnects the dialfrom the tip of the" p'li1g,"causing the releaseof the" relay A'2',Fig;2'and the closure of an energizing circuit for relays C2 and B43,throught'he right hand Winding of relay C 2,re lay 'B'43 and relay A2'.Relay A-2*it Willbe remembered, releases under this-conditibn and inretracting its left'arrna ture" opens the bridge to the distant ofic'e'includin rela"I+-2'leavin onl the olarized -relay 2 bridged across thetrunk froin 'upp'ertalking conductor 212, Fig. 2,

conductor 2ll, polarized relay F2, con

ductoi 210,"iniier right armature andfront contact of relay B' 2,conductor 209, con ductor2 08, left hand vvin'ding of relay C 2,armature and front contact of relay C2,

conductor 207, outer left'arrnat ure and back contact ot relayt H'-2,conductors 206 to lower talking "conductor 205'. The reversal ofthedirection er current in the talking conductors due to the operationof relay F3 (Fig. 3) causesthe'relay F-2 to operate, closing thefollowing circuit for relay 'G 2';" o1e of battery,relay G-'2, con

ducto-r' 224, contact 225 of relay F-2, corn 2 ductors"22 6, 227, 228,inner left armature andt'ront contact 'o't'relay B-2 to ground. Relay 'G-2'lock's itself up' o'ver the following'circui't: fre'e'pole'battery,relay G2 conductor224,conductor 229, front contactand armaturejaso,ofrelayi G 2, conductor 231, conductors 227, 228 to ground at the innerleft hand armature of relay I*1elay G-'2 connects the talking.conductors of Fig. 2 through to the talking conductors of Fig.1'Whereupo1'1 the calling supervisory frelay operates in series Wltllthe re lay {t -4, Fig, 4, and lights the supervisory lamplOO asa ringingsignal to the toll operator, Relay G 2 Fig. 2 cuts off the bridgeincluding" relays C-2 and A'2. Re-

lay opens the bridge containing; relay F-2. The'operator now operatesher ringing" kev RK which impressed alternating current-upon the talkingconductors and oper-j atesthe'alternating current relay C-3 in bridge ofthe trunk which in at-j the relay The polarized relay 8 3 is alsobridged across the trunk; Fin. 3, but the low frequency 16 to'20 cycleringing current open the-bridge containing relay S3. Re-

will irnin'ediately operate relay Which will by 'attrac'tlnp; its outerlett armature tively high frequency alternating current only, say 135cycles. Relay S3 will not therefore release relay R-3 which is nowenergized from ground on the sleeve wire 31 1-. Relay R-3 is at thistime holding open. the circuit of relay H3 for a purpose which willlater appear. To guard against a momentary opening of the back contactof relay S-3 releasing relay 13-3, relay lt-3 is made slow to release asshown. melay lfi3 in attracting its right armature opens the circuitheretofore traced, which has been holding relay F 5, Fig. 5, energized.Relay F5 in retracting its armature 53? connects ringing current to thecalled line through its own upper windin This ringing current isautomatically continued until the called party removes his receiver,resulting in the increase in the current through the upper Winding ofrelay F-5 causing thesame to operate removing the ringing current. Theattraction of the armature of this relay again closes the lockingcircuit for the same over control conductor 500. The extension of thetip and ring conductors by relay F5 to the called line operates relay A3over the winding of which talking current is fed to the called line.Relay A3 in operating energizes relay 13-3 which in attracting its righthand armature applies ground to the control conductor 315 to hold uprelay F5, Fig. 5. Relay in attracting its left armatures closes a bridgeacross conductors 306, 313 to hold up relay 1 1- 1, and opens theconnection of battery through the windings of relay A.- 1, Fig. 5, tothe talking conductors, leading back to the operators position whichcauses the deenergization of supervisory relay B 13. This relay inretracting its armature extinguishes the supervisory lamp 100 whichnotifies the operator that the subscriber has responded. Talking currentis fed to the called line over the windings of relay A--3 and therepeating coil 309. This talking circuit is a standard repeating coiltransmission circuit used in long distance connections. Talking currentis fed to the other line from the distant exchange. Durin conversationthe trunk leading from the lett hand windings of repeating coil 309through the right hand winding of the re peat? g coil (not shown) at thedistant office is dry, in accordance with standard practice. Theoperator may now request the subscriber at the substation'shown in Fig.5 to deposit the necessary coins in the coin box which may be of thetype shown in said Patent 19 13219, issued November 5, 1912 to O. F.Forsberg. These coins in passing tl'irough the box strike go ngs wherebythe operator is informed of the denominations of the coins inserted.When she is satisfied that the proper coins have been deposited shepicks up her plug P Fig. 1 and inserts it into the jack 133, and closesthe leftgcontacts of switch 135 which grounds the ring of the plug, thisresulting in the energization of relay 134. Relay 13 1 in operatingenergizes relay 130. Relay 130 in operating applies high frequencyalternating current, which may be of 135 cycles per second, to the trunk131, 137, which operates the alternating current relay S3, Fig. Thisrelay in operating removes the shunt from about relay (i -3 which inoperating grounds conductor 306 leading to the wind-- ing of relay A l,Fig. 1-, which is connected to battery. This is to prevent the releaseof the connection if the subscriber should hang up his receiver at thistime since relay 130, Fig. 1, in operating opens the loop circuit overwhich the relay AA was held over the cord. Alternating current relay S3in operating releases slow marginal relay R3, which in closing its backcontact energizes relay H3, this circuit including armature and frontcontact of relay F3 now energized. Relay H3 in at tracting its innerright armature operates relay K3 and in attracting its outer rightarmature extends the source of 110 volt collect current through thefront contacts of the relay K3, to the trunk conductors 322, 318. r hiscurrent passes over the talking conductors, Figs. r and 5 to groundthrough the polarized magnet 1 -5, Fig. 5. .Vheu the polarized magnet Ta; operates and collects the coins, it opens the contact 538 in the coinbox to remove the polarized magnet from the talking circuit.

If on the other hand the deposited coins are to be refunded, theoperator closes the right contacts of switch 135, Fig. 1. This not onlygrounds the sleeve of the plug P but also the tip of the plug, resultingnot only in the operation of the relays 134: and 130, but also relay 150which in operating bridges a retardation coil 138 across the trunkconductors 131 and 137. As before the high frequency alternating currentfrom the source 136 causes the operation of the relay H3. Due however,to the presence of the bridge containing retardation coil 138, Fig. 1,the shifting relay N3 operates, its circuit including the left-handarinatures and front contacts of relay E3, the talking conductors, Figs.2 and 1, and the bridge referred to. Relay N3 shifts the conductor 339leading to the front contact of the relay H-3 from the collect source ofpost tive current to the refund. source of negative current.Consequently refund current is transmitted over the line to operate thepolarized magnet P-5 in the coin box in the substation in the otherdirection to refund the coins and open the contact 538. The alternatingcurrent relay (3-3 which will be remembered operates to cause theringing operatlon of the connector to take place, Wlll reac es notoperate on the 135 cycle current for the reason that it is mechanicallyslow to operate and its electrical characteristics are such that it willnot respond to such high frequency alternating current.

ssiuning now that the desired line when selected by the connector isbusy. In that case the test multiple 526 5 is grounded. lVhen test wiper527 is set on the buy multiple 526, ground. is extended .over brush 527,conductor 528, contact 5&0 of :relay E5, conductor 54.1, armature 542and back con tactiof relay 1-1-5, conductor 5&3, relay G 5 to free poleof battery. Relay -G5 energizes and when E5 releases as the unitsimpulses terminate locks itself up over the following circuit: free poleof battery, relay G .5, conductor 543, armature 5&2 and back contact ofrelay li -5,, conductor 5&1, make before break contact 544 of relay E;5,, right armature and front contact of relay G-G, conductor 531,conductor 55-15 to ground at the armature 516 and front contact of relayB.5. Relay ,in the case of a local call connects busy tone from thesource 5525 to the calling line. In the case of a toll call this lousy:tone is not used, a flashing signal being given to $116 operatorinstead, as described. Due :to the operation of :relay relay ,cannotoperate. Consequently, relay iliI--.5 is not energized to .open thecircuit of relay .D3 .3 as described in the case of .an idle line.inasmuch as relay D3 remains energized, relay 1 3, whose circuitismaintained open at the outer right armature and back contact of relay is:not operated and no current reversal in the trunk zleading back to theoperator s position ioccurs. Polarized relay Ffi2 Fig. 2, is notoperated in this case and relay G 2 remains inert. .Since the relay E-2is locked 11p .at-this time and relayGr2 is inert, when the operatorrestores her dialing .key 'DZK .a circuit is closed from interrupter 233of 120 impulses per minute to shunt out resistance 200 to cause thesupervisory relay B--i8 to Jfiash the lamp 100, 120 ii mes per minute,which indicates to the op erator that the selected line is busy,whereupon. she pulls out the plug TT from the trunk switching jack TSJwhich results in the release of all switches and the normal condition ofall the apparatus including :the various looked up relays.

During the conversation the called 3511bscriber by moving his hook upand down causes the supervisory lamp 100 at :the ,toll operatorsposition to flash as in manual practice without releasing the switches.This is apparent from the preceding description inasmuch as relay l b- 3Fig. 3 isin circuit with the called line andeach time it attracts "itsarmature it operates the relay the supervisory relay ,B43 and putsbridge across-the relay A& to hold it operated. .When the calledsubscriber replaces his; receiver the lamp 1().O ,at thetoll opere atorsposition Fig. 1 is lighted. Theoperato-r may rering the subscriber ifnecessary iif sheicl-esires to recall him by actuating her ringing keyBK which-operates relay C to operate which in attracting its right handarmature again releases relay F Fig. 5 which initiates the automaticringing operation. The; control or this relay,F5;is removed from therelay E-B by the attraction of the right armature of relay when thecalled subscriber responded and is restored to the relay E3 andconsequently to the operator when the called subscriber replaces thereceiver and rleenergizes ire'lay B.3.

lWhen the operator desires to break down the connection after thecal-led subscriber has replaced his receiver, she reinovesith-e plug TTfrom the toll switching jack TSJ. This releases relay A.4 Fig. 4 whichcauses the restoration ofall the switches. If, however, the operatorpulls out the plug while the called subscriber still has his receiveroff the switch hook, the switches are not released.

Assuming, however, that the called subscriber has replaced hisreceive-r, when the operator removes the plug, relay A4 releases,dcenergizing relay B-4-. Relay B?& in retracting its router leftarmature -removes ground from the sleeve conductor 4:51 leading over thesleeve conductor 314 (to the re lease relay of the incomingselector ISwhich thereupon causes release of such selector in the well-knownmanner. The removal of ground from conductor ;&03, by the retraction ofright hand armature of relay B4lreleases relay D land the retraction of.the right hand armatures of relay A-4 and inner left armature of relayBe -encloses the circuit of the release 1magnet52 of the tolltransmission selector as follows: free pole of battery, magnet 425,10wercontact of off normal switch 415, conductor 41153, back contact andinner left hand armature of relay B4c to ground at the right handarmature and back contact of relay A4 The slow relay F-4 flfil'lelfig'lZeCl in parallel with the release magnetra-nd opens thecircuit to the test brush 426 during restoration at its lowermostarmature. At its armature 454 it short cir cui;t s the lefthand Windingof relay A-i. At its upper armatureit closes a locking circuit foritself .which ;is opened when the off -I Q, '1na;l switch assumes itsnormal position. Hllieopening/of the circuit of the tip and ringconductors 5 and 546 causes the release of relays A5 li -5, J. 5, Fig. 5which results in the closure of th circuit of connector release magnet546 free pole of battery, magnet e46, .lett hand 101 -11- tacttot oilnormal switch 520, *backcontact and lowermost armature of relay D 5,lower armatures and back contacts of relays B5 and A-5 to ground. Theconnector upon reaching normal position restores the oil normal switch520.

The relay l I S is provided to permit the toll operator to apply ringingcurrent to a selected private branch exchange line to signal theoperator thereat. This relay is operated when relay E3 is operated due'to the actuation of the ringing lrey by the toll operator. In privatebranch exchange working the called subscriber may hang up his receiver,but due to the'hridge at the P. B. X. operatofis board the relay A lremains operated and thus no disconnect signal is given to the tolloperator.

What is claimed is 1. In a telephone system the coinl'iination ofsubscribers lines, an operatofls position. means including tollswitching trunks and automatic switches for extending a call from saidposition to a subscribers line, a coin box at the substation of saidline having a coin disposal magnet, collect and refund current sourcesassociated 'with one of said trunks, a coin current applying relayassociated with said trunk, an alternating current source at saidposition, a manual switch at said position for applying alternatingcurrent from said cource to said trunk to cause the operation of saidrelay to apply current from one of said sources to the connectedsubstation to operate the coin disposal magnet in one manner, a shiftingrelay also associated with said trunk, and a manual switch at saidposition for operating said coin current applying relay and also saidshifting relay, the latter substituting the other coin current source tooperate the coin disposal magnet in another manner.

2. In a telephone system the combination of telephone lines, aconnection comprising toll trunks and automatic switches. a coin box atthe substation of the COll'l'lBCllQtl line having a coin disposalmagnet, a toll operators position, a pair of coin current; sourcesassociated with one of said trunks, a coin current applying relayassociated with said trunk, means including a manual switch at saidposition for operating the same, a shifting relay controlling theassociation of said sources with said trunk, a circuit for operating thesame controlled at alternate contacts or said coin current applyingrelay and including the trunk leading back to the toll position, andmeans at said position controlled by the operator for closing thecircuit or not, dependent upon which source is to be connected to theconnected subscribers line.

3. In a telephone system the combination of telephone lines, anoperators position, means including toll trunk lines and automaticswitches for extending connection to trunk one of said lines, a coin boxat the substation of said line having a coin disposal magnet, collectand refund coin current sources associated with one of said toll trunks,a coin current applying relay associated with said trunk, a shiftingrelay for controlling the connection of said sources to said trunk, analternating current source associated with said position, a manualswitch for applying alternating current from said source to said tocause the operation of said coin current applying relay to apply currentfrom one of said sources to operate said coin disposal magnet in onedirection, a bridge for said trunk, an impedance device therein, and asecond manual switch for applying alternating current from said sourceto said trunk and also closing said bridge thereacross to operate saidshifting relay to cause said coin current applying relay to applycurrent from the other source to said magnet.

4. In a machine switching telephone system, the combination of a numberof o'fiices, a. toll position at one office, automatic switches andtrunks at another oiiice, subscribers lines terminating in said lastoffice, two-wire interofiice trunk over which said switches are set tocomplete a connection to one of said lines, coin boxes at thesubstations of said lines having coin disposal magnets, sources ofcollect and refund current at said automatic office, a coin currentapplying relay at said automatic ofice operated from said toll positionover said two-wire interoiiice trunk to cause current from one of saidsources to be applied to the coin disposal magnet to operate the same inone direction, a shifting relay at the automatic oihce, and meanscontrolled by the toll operator including a circuit over saidinteroi'lice. trunk for also causing the operation of said shiftingrelay to cause current from the other source to be applied to the coindisposal magnet to operate the same in another direction.

5. In a machine switching telephone system, the combination with anumber of oflices, a toll position at one otlice, automatic switches andtrunks at another office, subscribers lines terminating in said lastoffice, a two-wire interoflice. trunk over which said switches are setto complete a connection to one of said lines, coin boxes at thesubstations of said lines having coin disposal magnets, sources ofcollect and refund current at said automatic oflice, of a pair of relaysat said automatic oiiice, one arranged to shift the connections of saidsources, and the other to cause the extension of said connections to thetrunk leading to the connected line, a bridge for said trunk, aretardation coil therein, and manual means at the toll office for eitherapplying alternating current to operate said latter relay to causecurrent from one source to be applied to the connected line, or forapplying alternating current and also a bridge containing a retardationcoil across the trunk to permit said first mentioned relay also tooperate and shift the connections to the other source.

6. In a machine switching telephone system, the combination with anumber of of fices, a toll position at one ofiice, automatic switchesand trunks at another office, subscribers lines terminating in said lastoffice, a two-wire interofiice trunk over which said switches are set tocomplete a connection to one of said lines, coin boxes at thesubstations of said lines having coin disposal magnets, and a source ofcollect current at said automatic office of an alternating cunrent relayin the trunk at said automatic office arranged when operated to causethe extension of said source to the trunk leading to the connected line,and a key at the toll position for applying alternating current to saidinteroffice trunk to operate said relay.

7. In a machine switching telephone system, the combination with anumber of offices, a toll position at one oflice, automatic switches andtrunks at another ofiice, subscribers lines terminating in said lastoffice, a two-wire interoffice trunk over which said switches are set tocomplete a connection to one of said lines, coin boxes at thesubstations of said lines, coin disposal magnets therein, and a sourceof collect current at said automatic ofiice, of an alternating currentrelay in the trunk at said automatic office, a relay operated thereby tocause the ex ension of said source to the trunk leading to the connectedline, and a key at the toll position for applying alternating current tosaid interoffice trunk to operate said alternating current relay.

8. In a telephone system, an operators position, a trunk, twoalternating current relays bridged thereacross, one adapted to respondto high frequency alternating current only, and the other to lowfrequency a ternating current only, a. coin current charging circuitcontrolled by one relay, and a ringing circuitcontrolled by the other,sources of current of high and low frequency at said position, andmanual means controlled by the operator thereat for impressing currentfrom said sources on said trunk to selectively operate sald alternatingcurrent relays.

9. In a. telephone system, an operators position, a trunk, twoalternating current relays bridged thereacross, one adapted to respondto high frequency alternating current only, and the other to lowfrequency alternating current only, a slow-to-release relay, a circuittherefor including a back contact of said high frequency relay, a coincurrent applying relay, a circuit therefor including a back contact ofsaid slow relay, a relay adapted to be operated by the operation of saidlow frequency relay tocause ringing current to be applied to the trunk,sources of high and low frequency current at said position, and manualmeans controlled by the operator for impressing alternating current fromsaid sources to said trunk to selectively operate said alternatingcurrent relays.

10. In a telephone system, an operators position, a distant office, atwo-wire trunk leading from said position to said distant office, twoalternating current relays bridged across said trunk at the distantoffice, one adapted to respond to high frequency alternating currentonly, and the other to low frequency alternating current only, a coincurrent charging circuit controlled by one relay, and a ringing circuitcontrolled by the other, sources of alternating current of high and lowfrequency at said position, and manual means controlled by the operatorfor impressing current from said sources on said trunk to selectivelyoperate said alternating current relays.

11. In a telephone system, firstand second offices, an operatorsposition at said first oflice, a line terminating at said second ofiice,a trunk interconnecting said offices, automatic switches at said secondoffice, means at said first office for controlling said automaticswitches over said trunk to interconnect said trunk andsaid line, asource of current, a. coin disposal magnet associated with said line, asource of alternating current at said first office, means. forconnecting said alternating current source to said trunk, and a relayresponsive to alternating current received over said trunk from saidsource for connecting said first men tioned source of current to saidline to control said magnet.

In witness whereof, I hereunto subscribe my name this 21st day ofDecember A. D., 1920.

HENRY L. HOFFMANN.

